This patient's clinical presentation (headaches, ataxia, loss of grip strength, and loss of pain and temperature sensation in a cape-like distribution) and imaging findings (MRI showing low-lying cerebellar tonsils protruding through the foramen magnum) is consistent with a diagnosis of Arnold-Chiari type 1 malformation.
Arnold-Chiari type 1 malformation is a herniation of the cerebellar tonsils through the foramen magnum. This is a congenital process that may not become symptomatic until adulthood. The symptoms of a type 1 malformation, chronic headaches and ataxia most commonly, are due to impaction of the foramen magnum, cervicomedullary junction compression, and interruption of CSF flow. Syringomyelia is associated with this condition and presents, as in this case, as loss of pain/temperature sensation in a cape-like distribution, and motor weakness in the hands. Patients who are minimally symptomatic without syringomyelia can undergo conservative treatment with medical therapy; however, severely symptomatic patients benefit from surgery to decompress the cervicomedullary junction and restore normal CSF flow.
Susman et al. review the diagnosis of Arnold-Chiari malformations. Type 1 malformations involve cerebellar displacement into the spinal canal, with hydrocephalus and syringomyelia occurring in some cases. Type 2 typically manifests with severe hydrocephalus and myelomeningocele. The diagnosis of type 1 malformations is often difficult due to the variable and often subtle presenting symptoms. History and physical, neurologic examination, and MRI evaluation are necessary to make and confirm the diagnosis of a type 1 Arnold-Chiari malformation.
McVige et al. discuss the imaging evaluation of type 1 Arnold-Chiari malformations. Cranial and spinal MRI is most commonly used to identify the degree of tonsilar descent and to document either the presence or absence of a syringohydromyelia. Cine-MRI is becoming a popular way to track the evolution and development of these malformations; cine-MRI is an imaging study that is synced with the patient's heart rhythm that allows for visualization of the flow of CSF through the foramen magnum. Pre-operative imaging is essential to offer a baseline for comparison and evaluation of post-operative progress.
Figures A and B are sagittal cuts of patient with an Arnold-Chiari malformation type 1 and associated syrinx; note the herniation of the cerebellar tonsils through the foramen magnum in both Figures A and B as well as the syrinx in the thoracic spinal cord shown in Figure B. Illustration A summarizes the spectrum of Arnold-Chiari malformations from Type 1 through 4; note the Dandy-Walker spectrum is also present, as this is in the differential diagnosis of an Arnold-Chiari malformation. Dandy Walker syndrome involves agenesis of the cerebellar vermis with enlargement of the 4th ventricle. Illustration B compares and contrasts type 1 versus type 2 Arnold-Chiari malformations.
Answer 2: Type 2 Arnold-Chiari malformation is more severe than type 1 and presents at birth. It is characterized by protrusion of the brainstem and cerebellum through the foramen magnum. Often accompanied by lumbosacral myelomeningocele.
Answer 3: Type 3 Arnold-Chiari malformation is rare and associated with occipital encephalocele (neural tube defect resulting in the protrusion of the brain and membranes through the posterior aspect of the skull).
Answer 4: Type 4 Arnold-Chiari malformation is rare and is characterized by cerebellar hypoplasia or, in severe cases, primary cerebellar agenesis; often this condition is not compatible with life.
Answer 5: Budd-Chiari syndrome is occlusion of the hepatic veins through thrombosis or external compression (such as by a nearby tumor). It presents with abdominal pain, ascites, and hepatomegaly.
Susman J, Jones C, Wheatley D. Arnold-Chiari malformation: a diagnostic challenge. Am Fam Physician. 1989 Mar;39(3):207-11.
PMID:2923030 (Link to Abstract)
McVige JW, Leonardo J. Imaging of Chiari type I malformation and syringohydromyelia. Neurol Clin. 2014 Feb;32(1):95-126.
PMID:24287386 (Link to Abstract)